A wireless communication system comprises of at least a transmitting apparatus and a receiving apparatus. The transmitting apparatus contains one or more antennas for transmitting one or more signals after modulating one or more baseband sub-symbols. The sub-symbols may be modulated by using modulation schemes such as PSK, QAM, and the like. The transmitting apparatus scans the available spectrum and then transmits the signal with a particular channel bandwidth for efficiently utilizing the available spectrum. A multiplexing technique such as orthogonal frequency division multiplexing also known as OFDM may be utilized to achieve higher data rate and to mitigate defects such as inter-symbol interference and fading caused due to multi-path delay spread. The receiving apparatus on the other side receives the OFDM modulated signal and thereupon identifies the channel bandwidth of the transmitted signal and demodulates the received signal into a plurality of individual PSK/QAM sub-symbol. The transmitting apparatus and the receiving apparatus communicate with each other based on various protocols and specifications including IEEE 802.11, Bluetooth, Advanced Mobile Phone System (AMPS), Global System for Mobile Communications (GSM), Code division multiple access (CDMA), Local Multipoint Distribution Service (LMDS), Multichannel Multipoint Distribution Service (MMDS), and the like.
In recent past, the IEEE 802.11 and its various versions commonly known as Wi-Fi have emerged as one of the most prominent wireless technologies for creating a wireless local area network (WLAN). The IEEE 802. 11 standards also play an important role in the future fourth-generation wireless and mobile communication systems. The development of 802.11a standard introduced orthogonal frequency division multiplexing (OFDM) to 802.11 standards, with data rates up to 54 Mbps in 20 MHz channel bandwidth. Subsequently, the 802.11g amendment incorporated the 802.11a OFDM PHY in the 2.4 GHz band. With the adoption of each new PHY, 802.11 standards have experienced a five-fold increase in data rate. This rate of increase continues with High Throughput (HT) IEEE 802.11n with a data rate of 300 Mbps and 600 Mbps in 20 MHz and 40 MHz channel bandwidth respectively.
To meet the increasing demand for higher throughput, the IEEE 802.11ac standard has been developed for facilitating Very High Throughput (VHT) wireless LAN. IEEE 802.11ac enhances the data rate beyond 1 Gbps in 5 GHz band and supports 80 MHz channel bandwidth option. IEEE 802.11ac supports 80 MHz channel bandwidth option in addition to 40 MHz and 20 MHz channel bandwidth options of IEEE 802.11n and IEEE 802.11a. Moreover, IEEE802.11n/ac introduces a channel bonding technique for efficient utilization of the spectrum. In channel bonding technique, available channel bandwidth i.e. 20 MHz or 40 MHz or 80 MHz is efficiently utilized either by using full channel bandwidth or partial bandwidth of the total channel bandwidth depending upon the availability of the spectrum. For instance, in case of 40 MHz channel bandwidth, two 20 MHz channels are bonded together. One of the 20 MHz channel is called a primary channel and the other 20 MHz channel is called a secondary channel. IEEE 802.11n/ac recommends different modes of channel offset to transmit PHY Protocol Data Unit (PPDU) independently in primary channel or by combination of primary and secondary channel by channel bonding technique. The 20 MHz channel bandwidth has only one mode of channel offset called CH_OFF_20. The 40 MHz channel bandwidth has five modes of channel offsets namely CH_OFF_20, CH_OFF_40, CH_OFF_40_NON_HT_DUP, CH_OFF_20U and CH_OFF_20L. Further, for 80 MHz channel bandwidth there exist seven possible modes of channels offset namely CH_OFF_20, CH_OFF_40, CH_OFF_40_NON_HT_DUP, CH_OFF_20U, CH_OFF_20L, CH_OFF_80 and CH_OFF_80_NON_HT_DUP.
At the receiver end, IEEE 802.11 ac compliant receiver apparatus is tuned to operate in one of the three RF bandwidths i.e. 20 MHz, 40 MHz or 80 MHz. While the receiving apparatus receives a radio signal, identifying the proper channel bandwidth and channel offset used by transmitted orthogonal frequency division multiplexing (OFDM) signal is crucial for successfully decoding a data packet. Thus, it is necessary to determine the channel bandwidth and channel offset of the received radio signal and perform demodulation according to the relevant channel bandwidth and channel offset. The traditional methods of channel bandwidth and channel offset identification used by receiver apparatuses are based on estimating frequency and timing offsets in each of the primary channel and secondary channel. The estimation algorithms provided by the present state of art are performed before channel equalization, due to which performance of these identification/estimation algorithms are highly vulnerable to frequency selectivity of the channel.